Professor Erno Rubik is the inventor of the well-known Rubik's cube described in HU-B-170062 (1976). It is based on the idea of providing a body made up from one or more sets of equivalent but identifiable pieces which are interconnected so that groups of pieces are relatively rotatable about three orthogonal axes. The pieces can exchange positions while the external shape of the body remains unchanged. Solutions of the puzzle are disclosed in a book by Tom Werneck, "Der Zauber-Wurfel", Wilhelm Heyne Verlag, 1981 (ISBN 3453-41449-7), the disclosure of which is incorporated herein by reference. Although the most popular form of the puzzle was a 3.times.3.times.3 cube, it was also produced as a 2.times.2.times.2 and 4.times.4.times.4 cube. A modified version of the cube was also produced in which the pieces were cut-off diagonally to give a puzzle which was octohedral when viewed in plan and in which the external shape of the body could be broken up by moving the pieces. Although Professor Rubik contemplated in his patent alternatives to a closed cube, and mentioned the possibility of the puzzle taking the form of another regular or semi-regular or amorphous body, semi-regular and amorphous bodies were not investigated. Instead, further developments in the field of logical puzzles lead to the Magic Pyramid described by Tom Wernick and to drum-based or sphere-based sliding bead puzzles.
WO 83/01203 (Torres) discloses a three-dimensional geometric puzzle having its pieces in a 3.times.3.times.3 arrangement, with the pieces shaped so that the external surface of the puzzle defines, in an undisturbed state of the puzzle, an identifiable three-dimensional object which may be inter alia a human head. The present applicants are not aware of any practical product having resulted from this disclosure, and believe that this lack of success was because the resulting puzzle was too difficult for acceptance by users.
The mechanical structure of a 3.times.3.times.3 Rubik's Cube has been described by D. R. Hofstadter in Scientific American, March 1981, pages 20-39 and is based on a central spider providing for rotation about three orthogonal axes, the central cube of each side face being attached to the spider by screws. An alternative internal mechanism for a 3.times.3.times.3 cube is disclosed in JP-A-55-3956 (1980). Like that of the original Rubik's cube, it requires internal screws to hold it together and additionally it has ball catches to define the positions where the pieces are accurately in register.
Commercially available 2.times.2.times.2 Rubiks cubes have a castellated spider mechanism based on a six-armed spider relative to which one piece is mechanically located in a fixed position and the remaining pieces are movable. Castellated members fit on the arms of the spider and each fit within two of the pieces. Three of the castellated members are rotatable on their respective arms and three of them are fixed. The mechanism has the advantage that the puzzle can be assembled simply by inter-engaging the individual internal parts and pieces and pushing the last piece into place, no screws or springs being required. An alternative internal mechanism for a 2.times.2.times.2 cube is shown in JP-A-55-8193 (1980) and has a central ball carrying six concentric part spherical guide members disposed in pairs along the three orthogonal axes and spaced a small distance above the surface of the ball. The attachment of the guide members to the central ball is by screws. Gaps are defined between adjacent pairs of follower plates. The movable pieces each have a part spherical plate which is trapped between the surface of the ball and a pair of the guide plates. The piece is connected to its trapped plate by a single peg which passes through the gap between the side plates. Because the piece is supported from the single peg, thick sections are needed where the piece and the peg join if adequate support and rigidity is to be obtained.